1. Field of the Invention
This invention generally relates to the field of an apparatus for supporting a wafer. More particularly, the present invention relates to an apparatus with a conductive material that moves inside a focus ring to improve the uniformity of the wafer edge plasma in the etching process.
2. Description of the Prior Art
The integrated circuits have been not only used anywhere in our daily life but also applied to computer industry, communication industry, and electronic consumer products. The process flows of making the integrated circuits are complicated and include hundreds of steps, such as deposition, photolithography, etching, diffusion, ion implantation, oxidation, thermal treatment process, etc. These processes will take about more than one or two months.
In addition, when the etching process proceeds, a focus ring is designed nearby an electrostatic chuck of a supporting apparatus to keep the quality of the etching uniformity of the wafer periphery. Most of the focus rings are made of quartz or Vespel consisting of polyimide. However, the material or thickness of the focus ring, sometimes, causes the inconsistency of the wafer edge Vdc. This situation leads to the poor uniformity of the wafer edge plasma and causes low energy of ion bombardment. Hence, the wafer may have the poor uniformity on its periphery after the etching process.
FIG. 1 illustrates a well-known apparatus for supporting a wafer in semiconductor process and the apparatus includes an electrostatic chuck 100 and a focus ring 110. The upside surfaces of the electrostatic chuck 100 include an upside surface 120 of a central circle and an upside surface 130 of a first ring edge, wherein a wafer is placed on the upside surface 120 of the central circle. The upside surfaces of the focus ring 110 include an upside surface 150 of a first ring and an upside surface 160 of a second ring, wherein the upside surface 150 of the first ring has the same height and is close to the upside surface 120 of the central circle, and a bottom 140 of the focus ring 110 is fixed on the upside surface 130 of the electrostatic chuck 100.
When a wafer 170 is placed on the upside surface 120 of the central circle of the electrostatic chuck 100, the wafer 170 is attached to the upside surface 120 of the central circle by applying DC power to the electrostatic chuck 100 to generate electromagnetic force. The ion energy of plasma beams 180 above the wafer 170 is stronger than those above the upside surfaces 150 and 160 because of the material and thickness of the focus ring 110 when a 1500˜2500 Vdc and a RF power are applied to generate a self-bias voltage. This affects the uniformity of the wafer 170 edge Vdc, leading to the inconsistency of the wafer 170 edge plasma and making the ion bombardment different energy, and then produces the poor uniformity of the wafer 170.